Charged particle beam irradiation apparatuses are known, which emit a charged particle beam such as a heavy particle beam to a diseased part of a patient with a cancer or the like. A charged particle beam irradiation apparatus is an apparatus which generates a charged particle beam at a beam generation device, accelerates the charged particle beam at a beam acceleration device, transports the accelerated charged particle beam through a beam transport device, and emits the accelerated charged particle beam from a beam irradiation device to the diseased part in a treatment room. The beam irradiation device emits the beam in accordance with a three-dimensional shape of the target diseased part. The beam irradiation device includes two pairs of scanning electromagnets, for example a pair of horizontally scanning electromagnets and a pair of vertically scanning electromagnets arranged in series, and scans charged particle beams in two directions that are perpendicular to each other.
In order to emit beams to cancers in various body parts and with various sizes, the range of irradiation (irradiation field) is preferably as broad as possible. Roughly speaking, there are two ways for broadening the irradiation field. First, series-connected two pairs of scanning electromagnets are located at a great distance from the patient to whom the charged particle beams are emitted. Second, the magnetic field strength of the outputs from the two pairs of scanning electromagnets is increased, or the axis length is elongated.
If the series-connected two pairs of scanning electromagnets are located at a great distance from the patient in order to secure a broad irradiation field, a great space is needed to install the charged particle beam irradiation apparatus. Therefore, a large housing may be needed for the apparatus.
On the other hand, if the magnetic field strength of the outputs from the scanning electromagnets is increased, or the axis length is elongated, the magnetic field generation efficiency of the scanning electromagnets downstream in the beam movement direction is lowered. Therefore, the irradiation field may not be sufficiently obtained.